Bacterial Ammonia Causes Significant Plant Growth Inhibition

Many and complex plant-bacteria inter-relationships are found in the rhizosphere, since plants release a variety of photosynthetic exudates from their roots and rhizobacteria produce multifaceted specialized compounds including rich mixtures of volatiles, e.g., the bouquet of Serratia odorifera 4Rx13 is composed of up to 100 volatile organic and inorganic compounds. Here we show that when growing on peptone-rich nutrient medium S. odorifera 4Rx13 and six other rhizobacteria emit high levels of ammonia, which during co-cultivation in compartmented Petri dishes caused alkalization of the neighboring plant medium and subsequently reduced the growth of A. thaliana. It is argued that in nature high-protein resource degradations (carcasses, whey, manure and compost) are also accompanied by bacterial ammonia emission which alters the pH of the rhizosphere and thereby influences organismal diversity and plant-microbe interactions. Consequently, bacterial ammonia emission may be more relevant for plant colonization and growth development than previously thought.